build: add the Makefile command surface (D-27)

Every repo gets one at the root: help, plus test and lint where those exist.
The point is that a target name means the same thing in every repo, so an
agent or a person can act without reading the repo first.

Paths resolve here rather than in callers (D-10). python3 on this host is 3.8
and cannot parse these sources, and a bare pytest or ruff resolves only in a
login shell — so both are named explicitly through the venv, and a missing
venv fails with the command to fix it rather than a bare no-such-file.

Co-Authored-By: Claude <noreply@anthropic.com>

Makefile

@@ -0,0 +1,40 @@
+# webber — the repo's command surface (D-27).
+#
+# Multi-component, so this lives at the root and reaches down rather than
+# sitting inside webber-api/. The code, tests and tooling config are all in
+# webber-api/; sandbox-templates/ and sandbox.sh are the other half of the repo
+# and have no build of their own. Keeping one Makefile means `make test` means
+# the same thing wherever you are standing (D-27).
+#
+# Paths resolve here (D-10): `python3` is 3.8 on this host, and a bare `pytest`
+# or `ruff` resolves only in a login shell.
+
+API    := $(CURDIR)/webber-api
+VENV   := $(API)/.venv
+PYTHON ?= python3.12
+
+.DEFAULT_GOAL := help
+
+.PHONY: help
+help: ## Show this help
+	@grep -hE '^[a-z][a-z0-9_-]*:.*?## ' $(MAKEFILE_LIST) \
+	  | awk 'BEGIN{FS=":.*?## "}{printf "  \033[36m%-14s\033[0m %s\n", $$1, $$2}'
+
+.PHONY: setup
+setup: ## Create the webber-api venv and install dev dependencies
+	cd $(API) && $(PYTHON) -m venv .venv && .venv/bin/pip install -e ".[dev]"
+
+.PHONY: test
+test: ## Run the webber-api test suite
+	@test -x $(VENV)/bin/python || { echo "FAIL — no venv; run: make setup"; exit 1; }
+	cd $(API) && .venv/bin/python -m pytest tests/
+
+.PHONY: lint
+lint: ## ruff check over webber-api
+	@test -x $(VENV)/bin/ruff || { echo "FAIL — ruff not installed; run: make setup"; exit 1; }
+	cd $(API) && .venv/bin/ruff check .
+
+.PHONY: typecheck
+typecheck: ## mypy over webber-api
+	@test -x $(VENV)/bin/mypy || { echo "FAIL — mypy not installed; run: make setup"; exit 1; }
+	cd $(API) && .venv/bin/mypy .